Gigahertz frequencies are used in many electronic systems these days. In order to be able to measure gigahertz frequencies directly, a resolution of a few pico seconds is needed.
Often, accurate measurement of these frequencies is beneficial to the working of components of a system. For example, in communications systems, a key parameter for mixer performance is the quality of non-overlapping clocks.
Pulses too far apart will result in increased noise figure (output noise compared to ideal output noise when connected to matched sources at the standard noise temperature as would be understood) and/or phase noise. Similarly, pulses too close to each other may result in the mixer output being short circuited for the time interval in question, resulting in lower gain, as well as increased noise figure and increased phase noise.
Accurately knowing the duty cycle of the clocks in such systems would help achieve optimum performance.
One method of duty-cycle measurement in a system is to vary the duty-cycle shape and time until the desired performance is achieved. This is an example of indirect measurement, which is not desirable.
Another way of indirect measurement of the duty cycle is to charge a capacitor through a known resistor. This gives the integral average of the pulse, but does not provide information as to the exact pulse shape, rise/fall time or duty cycle.
Accordingly, there is a need to provide an accurate way of directly measuring duty cycles at higher frequencies, such as gigahertz frequencies.